1. Field of the Invention
The present invention pertains to a locking device. The invention more particularly concerns the external locking of a hub to a housing of an automotive clockspring.
2. Discussion of the Background
Devices are well known in the art for locking a hub to a housing of an automobile clockspring. An automotive clockspring is an electrical connector which electrically connects a rotatable airbag assembly mounted on the steering column to stationary crash sensors located elsewhere on the vehicle. An automotive clockspring typically includes a housing and a cover mounted to the housing so as to form a cavity therebetween. Rotatably mounted within the cavity is a hub. The clockspring housing is non-rotatably mounted to the steering column, while the hub is attached to the rotatable airbag assembly. Electrical cable is wound around the hub. One end of the electrical cable terminates at the stationary housing or cover and the other end terminates at the hub. The end of the electrical cable terminated at the hub is then connected to an electrical cable which connects to the airbag assembly. During use, the electrical cable is either spooled or un-spooled around the hub when the steering wheel is turned in one direction or the other direction.
When the clockspring is assembled to the steering column of the vehicle, the vehicle typically has its wheels in a neutral position, i.e., the wheels are in a straight forward position, not turned right or left. Thus, it is critical that the hub of the clockspring is rotationally positioned relative to the housing in a such a position that the hub is able to rotate in either direction in equal amounts. That is, the hub must be at its center or mid-span of travel position. Otherwise, if the clockspring is assembled to a vehicle where the hub has been pre-rotated a few rotations or degrees from center, then when the operator of the vehicle turns the steering wheel as far as possible in the one direction, the electrical cable coiled around the hub will be pulled out of the hub or the housing, the electrical cable will rupture, or the electrical cable will have its cross-sectional area reduced due to the applied tensile force, thus reducing its ability to properly carry the electrical signal. Therefore, the critical electrical connection between the airbag assembly and the stationary crash sensors would be lost.
One prior art solution was to have the assembly-person rotate the hub through all of the travel from one end of travel to the other end of travel. Then, the assembly-person would back off, or rotate, the hub away from one of the ends of travel by an amount equal to one half of the total number of rotations of full travel. Thus, the clockspring would be at its center or mid-span of travel position. At such a time, the assembly-person would mount the clockspring onto the steering column. Over time, labor cost became so high that the amount of time required to perform the assembly operation described above became prohibitive.
Due to the high labor costs, the automotive manufacturers required suppliers of clocksprings to deliver clocksprings that had hubs locked at the center or mid-span travel position relative to the housing. As such, a clockspring could be taken out of inventory and directly mounted to the steering column.
One prior art solution, known as an internal locking clockspring assembly, is exemplified by U.S. Pat. Nos. 4,886,460, 5,460,535, and 5,171,157; U.K. Patent Application No. GB 2250146; and European Patent Application No. 0195833. A common feature of these references is that they all lock the hub to the housing of the clockspring by way of parts or mechanisms forever or integrally attached to the clockspring. The internal locking clockspring assembly remains locked before installation, becomes unlocked when installed, and, typically, becomes locked again when removed from the steering column, such as for repair work. The internally locking clockspring assemblies perform adequately, but, due to the number of parts required to make the mechanism work properly, the cost, size, and weight of such clocksprings are relatively high. Thus, there is a need for an inexpensive, locking clockspring which is small and light in weight.
Another prior art solution, known as an externally locking clockspring assembly, is exemplified by U.S. Pat. No. 4,722,690, and European patent Application No. 0195831. A common feature of these references is that they all lock the hub to the housing of the clockspring by way of parts or mechanisms removable from the clockspring. The externally locking clockspring assemblies remain locked before installation. Then, just before or just after being installed onto the steering column, a removable locking part, device, or mechanism is removed from the clockspring, thus allowing the hub of the clockspring to rotate relative to the housing of the clockspring. The removable locking device is typically discarded.
An advantage of the externally locking clockspring assembly is that the external locking device does not take up valuable space when the clockspring is assembled on the steering column. Furthermore, the external locking device does not add weight to the clockspring since the external locking device is removed from the clockspring. Another advantage of the external locking clockspring is that it is relatively inexpensive, since it does not have as many parts as the internally locking clockspring assembly.
A disadvantage of external locking clocksprings is that the removable external locking device can be removed, the hub rotated away from center, and then the external locking device can be re-attached to the clockspring, resulting in a tampered clockspring. If a tampered clockspring is assembled on a vehicle, the clockspring may fail to properly conduct the electrical signal as described above. Such problems exist with one type of clockspring where the external locking device is a label or seal which attaches to part of the hub and to part of the housing. When the seal is removed, the hub can rotate. However, the seal can also be re-applied to the hub and housing after tampering with the clockspring. Additionally, European Patent Application No. 0195831 discloses an external locking device which includes a cup-shaped lock having a notched projection and a clip pin which engage the hub and the housing of the clockspring to prevent rotation therebetween. This reference fails also because the external locking device can be re-installed on the clockspring after tampering with the clockspring with no visible notice of tampering of the clockspring to the person installing the clockspring onto the steering column. Thus, there is a need for an external locking clockspring assembly where the external locking device can not be re-installed without indicating a notice of tampering or that only a person of authority be capable of re-installing the external locking device.
U.S. Pat. No. 4,722,690 discloses an external locking device which takes the form of a tab molded to the housing where the tab prevents the hub from rotating. The tab is connected to the housing via perforations. To allow rotation of the hub, the tab is removed from the housing. The structure of the tab prevents it from being re-attached to the housing. Thus, once the tab is removed, the clockspring must be mounted to the steering column or be discarded. Therefore, the externally locking clockspring assembly of U.S. Pat. No. 4,722,690 provides notice of tampering, however, the clockspring of U.S. Pat. No. 4,722,690 can not be salvaged or re-used if one of the clocksprings is taken from inventory and inspected for compliance to requirements of being positioned at the mid-span of travel or if the tab is inadvertently removed. Thus, there is a need for an externally locking clockspring which can have the external locking device re-installed in the clockspring provided the external locking device is re-installed by a person possessing the required skill, knowldege, and authority. Such re-intsallation is necessary after an external locking device is removed from a clockspring taken from inventory, where the clockspring is inspected for compliance with requirements, or after an external locking device has been inadvertently removed from the clockspring and needs to be re-installed, or after a clockspring has been removed from the steering column when repairs are made to the steering column.
Thus, there is a need for an inexpensive, reliable, small, external locking clockspring assembly which has an external locking device which can be re-installed under controlled conditions.